Several types of on-chip processors, such as for example high definition audio/video interfaces, must be protected with device-specific keys, available from the relevant interface licensing authority, for authentication and/or encryption. These device-specific keys may further be referred to with the term device keys. These device keys must be protected against disclosure, modification or cloning. On an applications processor, this includes protection against access to the device key for offline storage as well as run-time protection. Hence device keys are typically stored in arrays of on-chip one-time programmable non-volatile storage elements, such as on-chip fuse arrays, with access restricted to a dedicated co-processor, either via a private bus or a specially-protected private on-chip RAM. The device keys are typically programmed into the arrays of on-chip one-time programmable non-volatile storage elements by the manufacturer of the applications processor.
An applications processor with multiple video interfaces requires multiple device keys and therefore multiple on-chip fuse arrays, which may create scaling problems for the known approach. For example, a manufacturer of semiconductor devices may manufacture a single type of applications processor in multiple market segments via one or more original equipment manufacturers (OEMs). The OEM integrates the applications processor into some higher-level component, such as a consumer electronics device, according to an OEM design. Applications processors of the same type may thus be required to be suitable for use in a plurality of different OEM designs from one or more OEMs. For example, an applications processor may require up to six individual unique device keys of around 100 to over 2000 bits each for supporting the variety of OEM designs that the applications processor may be used in, and thus need at least six on-chip fuse arrays for storing all six device keys, which may correspond to over 12,000 fuses (six times over 2000 fuses). However, typical OEM designs need only need a subset of the video interfaces available on the applications processor, e.g. only one or two. Only one or two device keys are needed for these designs and the other four or five on-chip fuses of the total six on-chip fuse arrays would not be used. Also, some OEM designs may require device keys additional to the device keys programmed by the manufacturer, while known application processors do not allow easy handling and protecting device keys from different stakeholders. Known application processors may thus not be able to support OEM designs which require for example that keys licensed by a manufacturer must be protected against OEM-licensed software, and OEM-licensed keys must be protected against manufacturer's test patterns on field returns, while both keys licensed by the manufacturer and OEM-licensed keys need to be protected against end user software. Known application processors cannot support such requirements, as known applications processors may only offer a limited flexibility for storing and protecting various combinations of device keys licensed by multiple stakeholders.